The hip joint is the joint that connects between the thighbone and the hipbone of the pelvis in the body. The hip joint performs the most important function when a person sits or stands. The hip joint can be damaged by a pathological reason such as tuberculosis, an external wound, or the like. In order to cure the damaged hip joint, an artificial implant for a hip joint can be implemented by a surgical operation. Typically, an artificial implant for a hip joint includes a stem and an acetabular cup. The stem and the acetabular cup are fabricated from, for example, a body-friendly material such as a Ti alloy. The stem for the artificial hip joint is inserted into and fixed to the thighbone, and the acetabular cup is fixed to the acetabulum of the pelvis. A globe made of a ceramic or metal material is fixed to one end of the stem, and a bearing having a corresponding shape is inserted into the cup, such that the globe can be received and rotate in the bearing. The bearing has a concave hemispherical inner surface such that the globe fixed to the one end of the stem can rotate therein, thereby enabling the joint motion. The bearing is also made of a ceramic or polymer polyethylene material.
An approach for allowing bearings made of different materials to be selectively inserted into one acetabular cup for use is disclosed in U.S. Pat. No. 6,610,097.
In order for the ceramic bearing to be inserted into the acetabular cup, a taper portion is formed on the inner portion of the acetabular cup and on the outer circumference of the bearing.
In addition, in order for the polyethylene bearing to be inserted, several recesses are formed in the lower end of the acetabular cup, and a circular recess is formed along the inner circumference so as to be positioned above the recesses. In addition, several locking portions which are inserted into the recesses are formed along the circumference, and circular fixing portions are positioned above the locking portions such that the fixing portions are inserted into the circular recess.
However, when the ceramic bearing is inserted into the acetabular cup via the circular recess, the area in which the bearing adjoins the acetabular cup is reduced by the cross-sectional area of the circular recess. Therefore, the ceramic bearing can be easily broken, which is problematic.
In addition, the circular recess also causes the overall strength of the acetabular cup to be decreased, which is problematic.